This invention relates to an apparatus for and a method of generating (SH Shear Horizontal waves which are used) for probing internal structure of probing objects such as the earth's crust, a material, a living body and the like.
There have been developed various kinds of methods of probing or invetigating the internal structure of the shallow portion of the earth's crust, a material, a living body and the like. However, each method is not necessarily suitable for all probing objects because of the difference in probing objects and resolution. For example, CT (computerized tomography) used widely in the field of medical service is a probing method having a high resolution and reliability. However, there is a case that CT cannot be adapted for, due to the physical property and largeness of a probing object, a probing environment or the like. In the case of probing the internal structure of a body, or electromagnetic field, static electric field, static magnetic field, dynamic displacement, temperature, etc. are measured. Among them, a method of probing the internal structure of a solid body by measuring kinetically dynamic displacement, that is, displacement of elastic P waves (including velocity and acceleration of displacement) is often utilized for earthquake probing or ultrasonic probing because of its relatively high resolution.
In this case, P waves (longitudinal wave compressional wave) as elastic waves are mainly used, however, there may be many cases that S waves (transverse wave shear wave) are more effective. A conventional S wave generating device generates SV waves in addition to SH waves, and propagation pattern of the S wave is very complicated. Further, the P wave is generated at the same time. Therefore, in the survey in which S waves are generated by the conventional S wave generating device are used, a good S/N ratio is not generally obtained.